In most torque delivering power tools it is desired to continuously measure the torque delivered by the tool to e.g. a joint. In general the torque may be measured anywhere along the drive line from the motor to the output shaft.
In order to minimise the errors in the torque measuring it is beneficial to locate the torque transducer as close as possible to the output shaft. In some applications the torque transducer is even located on the output shaft. In such arrangements a wireless data transmission has to be provided between the torque transmitting output shaft and a control unit housed inside the tool or at a location close to the workplace of the tool.
A problem related to this is however that the torque transducer and the wireless data transmission will need space, and the space is very limited inside a power tool, especially around the output shaft.
In WO 2010/144048 A1 a power wrench is disclosed in which a circuit board is arranged in a cavity inside a shaft of the transmission between the motor and the output shaft. This arrangement reduces the space demands inside the tool housing. The torque transducer, which is comprised of a strain gauge, does however require a certain length of the shaft. Hence, it is still a desirable to improve the compactness of the power tool.
There is a need for a solution that provides a liable measurement of the torque, e.g. close to the output shaft, but which does not demand a lot of space inside the housing of the tool.